As reported by the New York Heart Association in 2008, heart failure was prevalent in 8.5 million patients in 2008 and this is increasing at an annual growth rate of 10.5%. Thus, by 2010 heart failure can be prevalent in an estimated 11.6 million patients. Further, and as reported by the American Heart Association in 2008, more than 1 million hospital discharges per year have a primary diagnosis of heart failure, the most common discharge diagnosis.
Patients admitted to the hospital with Congestive Heart Failure (CHF) symptoms from severe fluid overload usually have had fluid build-up without symptoms for days or weeks prior to admission. Detection of elevated fluid prior to symptoms could prevent admissions for “acute” decompensated heart failure. Also, many patients with CHF are inadequately diuresed at discharge (i.e., not enough fluid has been removed prior to discharge). This, typically leads to re-admission of the patient for CHF. The rate of rehospitalization for heart failure is very high; about 20% at 30 days after discharge, and about 30% at 60-90 days after discharge.
As is known to those skilled in the art, measurement of left ventricular filing pressure (LVFP) allows detection of CHF and helps assessment of the efficacy of therapy for CHF. Left ventricular pressure can be measured directly by placing a catheter in the left ventricle to obtain the end diastolic pressure (LVDEP) or indirectly by placing a catheter in the pulmonary artery to measure the pulmonary capillary wedge pressure (PCWP). It should be noted that measuring LV filing pressure using a catheter is generally considered the gold standard. The pulmonary artery catheterization (PAC) technique that is used to measure either LVFP or PCWP is considered an invasive surgical procedure. Thus, there are attendants risks and costs associated with such a technique and the reported complications include catheter migration, arrhythmias, pulmonary artery rupture, thrombosis, infection, bleeding and pneumothorax.
Physical examination of a patient has poor sensitivity for detecting elevated cardiac filing pressure, especially in patients with chronic heart failure. Some common aids use to help in the diagnosis of elevated LVFP include chest X-ray, serum biomarkers (BNP, pro_BNP) and echocardiography. These techniques have important practical limitations. Also, clinical and radiographic methods of detecting CHF are generally insensitive to alterations in LVFP.
There have been attempts made to develop a non-invasive method and system for estimating LVFP to allow for early detection and treatment of CHF, which has been shown to reduce the rate of hospitalization and mortality. A non-invasive method of assessing PCWP has been reported that uses the strain phase of the Valsalva maneuver. In a Valsalva maneuver, the subjects or patients perform a forced expiration into a closed tube or strain against a closed glottis. This results in a unique, well-described cardiovascular response, involving both a rise and fall in arterial pressure and a momentary opposite-direction change in right and left heart stroke volume. The effect of the Valsalva maneuver on blood pressure for a normal heart and a heart diagnosed with heart failure is shown in FIG. 1.
In this method a non-invasive pulmonary tonometer and a digital pulmonary monitor is used to continuously acquire arterial and expiratory pressure signals during a Valsalva maneuver. A software program also is used to analyze the arterial pressure signals and derive a LVEDP using a predictive algorithm. The tonomter is not easy to use and is located on the wrist or finger. While this system is not yet commercially available it is expected to cost in the tens of thousands of dollars. The tonometer also is not as widely used a technology as compared to some other medical devices.
Another reported non-invasive technique is referred to as impedance cardiography (ICG). In the ICG technique, four electrodes are placed around the neck and lower thorax and four electrodes are placed on the lateral surface of the abdomen. In this arrangement the outer sensors transmit current and the inner sensors measure impedance. The impedance being measured across the chest is related to fluid volume; thus it can be used to measure changes in fluid volume. However, such measurements do not reflect absolute measurements of LVEDP. The cost for such a device also is in the tens of thousands.
Thus, there is a continuing need to develop non-invasive systems and methods for assessing cardiac filing pressure, more specifically LV filing pressure. It also would be desirable to provide such a device that provides similar useful clinical information as prior art systems and methods. Such systems preferably would be less costly than prior art systems, would use a robust transducer and such methods would not involve or require a greater skill set than that required for user of prior art methods. Moreover, it would be desirable to provide a device or system whose operation is simple enough for a patient or the like to use at home.